1. Field
The present work relates generally to wireless communication and, more particularly, to OFDM (Orthogonal Frequency Division Multiplexed) wireless communication.
2. Background
FIG. 1 diagrammatically illustrates an OFDM receiver according to the prior art. After down-conversion to baseband, the signal is converted from analog to digital in the A/D converter 110, and processed by an FFT unit 111 to provide the values of the subcarriers for each OFDM symbol. A demultiplexer (“demux”) unit 112 then aggregates the modulation symbols. A pilot extraction unit 113 extracts pilots (or clusters of pilots) from the received modulation symbols (which also include data symbols).
At 114, a channel estimation unit derives a channel estimate from the pilots (or from averages of pilot clusters). One known method is to consider a region in time and frequency (also referred to as a tile) that contains four pilots (or pilot clusters), one for each of the following points in the region: (1) lowest frequency at earliest time; (2) highest frequency at earliest time; (3) lowest frequency at latest time; and (4) highest frequency at latest time. The pilot extraction unit 113 makes local complex channel estimates corresponding to each of these four time/frequency extremes. These four local complex channel estimates are provided at 118. (FIG. 2 shows an example of four local channel estimates P0-P3 associated with the four time/frequency extremes of a given tile.) The channel estimator 114 characterizes the local channel estimates at 118 as each having a first component that is constant, a second component that varies linearly with frequency, and a third component that varies linearly with time. By superposing these three components, a channel estimate for any time/frequency position within the region is obtained at 120.
In addition, an interference estimate 119 is obtained by interference estimator 115, which estimates a fourth component that is orthogonal to the aforementioned constant, linear in time and linear in frequency components. Demodulation/decoding unit 116 uses the channel estimate 120, the interference estimate 119 and the data symbols (provided at 117 by demux unit 112) to demodulate the signal into, e.g., log-likelihood ratios (LLRs). The unit 116 then decodes the demodulation result using a forward-error-correction (FEC) decoder, such as a Viterbi or turbo decoder, to produce at 121 a received version of the transmitted payload.
Exemplary embodiments of the present work provide heretofore unrecognized applications for the aforementioned local channel estimates produced at 118 by the pilot extraction unit 113.